Interlocking joint

ABSTRACT

An interlocking joint includes a hollow outer leg having three or more sidewalls which intersect to form at least three vertices, an inner leg member which includes at least three interconnected flanges each of which extend into one of the vertices, and securing means affixed to the inner leg that holds the legs in desired relative position by bearing on one or more sidewalls of the outer leg and thus urges certain of the flanges toward their corresponding vertices.

United States Patent [191 Martin INTERLOCKING JOINT [75] Inventor: FrankHerbert Martin, Holmdel,

[73] Assignee: Bell Telephone Laboratories Incorporated, Murray Hill,NJ.

221 Filed: July 2,1973

21 Appl. No.: 375,613

[52] US. Cl. 403/104 [51] Int. Cl. F16b 1/00 Field of Search 403/298,52, 109, 104, 403/205, 217, 382, 83; 52/656, 758 H, 475, 285

[56] References Cited UNITED STATES PATENTS 935,592 9/1909 Dougherty403/104 x 1,625,510 4/1927 Tredwell 403/52 July 23, 1974' 1,830,37011/1931 Mitchell 403/104 2,304,223 12/1942 Westrope 403/52 3,087,7684/1963 Anderson et a. 52/758 H Primary Examiner-Richard J. Scanlan, Jr.Attorney, Agent, or Firm-Barry H. Freedman [5 7] ABSTRACT Aninterlocking joint includes a hollow outer leg having three or moresidewalls which intersect to form at least three vertices, an inner legmember which includes at least three interconnected flanges each ofwhich extend into one of the vertices, and securing means affixed to theinner leg that holds the legs in desired relative position by bearing onone or more sidewalls of the outer leg and thus urges certain of theflanges toward their corresponding vertices.

12 Claims, 16 Drawing Figures PATENTEMmzamu SHEET 2 OF 6 3 N9 wm am c259Us 5 9w 2m @1 @1 i Q N 6R PAlENTEnJuLzsmu SHEET 0F 6 PATENTEUJUL23I974FIG/l 3 (E H23 SHEET 5 OF 6 FIG. /4

INTERLOCKING JOINT I BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates generally to an interlocking joint andmore particularly to such a joint in which an inner leg member iscontinuously adjustable in position with respect to an outer leg member,without the need for external locking mechanisms.

2. Description of the Prior Art 1 Numerous ways have been devised tosecure an inner leg member within an outer leg member, in a desiredcontact with the outer member, after the legs are placed in desiredposition. These arrangements are not always suitable, however, becausethe pins or bolts detract from the otherwise smooth appearance of theouter legs, and are subject to tampering or other damage because theyare at least partiallyextemal to the legs. Also, in some configurations,the leg positions are not continuously adjustable.

Some of the above problems are avoided by another series of prior artpatents relating to extensible tele-- scoping legs, which disclose aleaf spring used to urge a locking means attached to the inner leg intoengage.- ment with the inner surface of the outer leg. The locking meansmay be a pivotably attached dog or retainer which acts in a ratchet-likemanner. Accordingly, in

certain instances, it is necessary to first'move the legs to an extremeend position in order to disengage the retainer before making a desiredadjustment of position. Additionally, this type of mechanism is quitecomplicated and expensive, and is readily subject to malfunction.

Still another. approach known inthe prior art is'to use a leaf springwith barbs placed in a groove in the outer surface of an inner squareleg, which fits within an outer square leg. The spring creates frictionbetween the legs, holding them in desired position; the barbs 2" 4. thelocking-means is held in position'by the inner g member.

SUMMARYOF THE INVENTION Each of the foregoing and additional objects areachieved in accordance with the invention by an interlocking joint whichbroadly includes a hollow outer leg member having a-longitudinal axisand three or more side-walls which intersect to form at least threevertices, an inner leg member which includes at least threeinterconnected flanges each of which extends into a particular one ofthe vertices, and securing means atfixed to the inner leg that hold thelegs in a'desired relative position by bearing on one or more side wallsof the outer leg and thus urges certain of the flanges toward an arcuatespring having at least one simicircular lobe, or a locking pin. Ineither event, one end of the securing means is affixed to one flange ofthe inner leg member, and is positioned adjacent .a second'one of theflanges. The radius of the arcuate spring and the length of the lockingpin are approximately equal to the discuring means is affixed to theinner legbyextending it through a small hole in the interveningflange.The'

spring is dimensioned as previously indicated so that it assumes agenerally circular configuration upon insertion of each semicircle oneach flange engaging-or bearing on.a portion of the inner surface ofthe. outer prevent extraction once the legs are properly positioned.While this arrangement has certain advantages,

it alsohas several drawbacks. Most importantly, since Accordingly, therecan be no protrusions into the outer leg which would interfere with thespring. However, these protrusions are necessary if external panels,baffles or other similar items are to be fastened to the outer leg indesired locations. In addition, this approach suffers from the fact thatthe spring locking means is not secured to the inner leg, therebysubjecting it to misalignment or possible loss.

In view of the foregoing difficulties, it is the broad object of thepresent invention to provide an improved interlocking joint. Specificobjects include a joint design in which:

1. The locking means is simple and inexpensive, and fully containedwithin the leg members,

2. the leg members are continuously adjustable relative to each other,

3. the locking means does not interfere with protrusions into the outerleg necessary to secure other items thereto, and

leg. This engagement or hearing aforce radially urges certain flanges ofthe inner leg into contact with vertices of the outer .leg, therebylocking or securing-the legs in a desired relative position. 7 v i Inanother embodiment, thev outer hollow leg is triangular in shape, andthe inner leg iseither T or -Y- shaped in cross section. In the latterinstanee, the arcuate spring member is deformed from the previouslydescribed planar configuration, so that the semicircles intersect at anacute angle which corresponds to the angle formed by adjacent flanges.

The advantageous design, in accordance with the invention, of aninterlocking joint as above described, has

I many advantages. First, since, the locking means in accordance withthe invention can be fabricated, for example, from a portion of oneconvolution of a helical wire spring or from a simple length of wire, itis thus quite simple and inexpensive. Second, by virtue of the fact thatthe spring is affixed to the inner leg, as for example, by insertionthrough an aperture therein, .it is held in desired position and cannotbe lost or misaligned. While the lockingjmean's is internal to the outerleg, it does not interfere with any protrusions that might be requiredinto that leg, because of theadvantageous use of an inner leg havingthree or more flanges which contact the outer leg only at its vertices.The leg design in accordance with'the invention also permits continuousadjustment of relative leg positions.

3 BRIEF DESCRIPTION OF THE DRAWING Further advantages and features ofthis invention will be more readily understood from the followingdetailed description, when read in light of the accompanying drawing inwhich:

FIG. 1 is a perspective view of an interlocking joint in accordance withthe instant invention, in a disassembled condition;

' FIG. 5 is anend view of the interlocking joint of FIG.

FIG. 6 is a perspective view similar to FIG. 1 showing an interlockingjoint with an alternate locking means, in disassembled condition;

FIG. 7 is a partially cut-away front view of the jointof FIG) 6 in whichthe leg members are fully assembled;

FIG. 8 is an end view of the interlocking joint of. FIG. 7; f

FIG. 9 is a perspective view of another embodiment of an interlockingjoint in accordance with the invention;

' FIG.= 10- isan end view of the joint of FIG. 9;

FIGS. 1 115 are end views of other configurations of interlocking jointsin accordance with the invention; and a FIG. 16is a perspectiveview of acubicle fabricated using-a number of interlocking joints in accordancewith the invention, with insets showing portions of the joints indetail.

DETAILED DESCRIPTION- Details of the invention will best be understoodby first considering one embodiment thereof, depicted in various viewsand conditions in FIGS. 1-5, in which the same numerals are used toindicate similar parts. FIG. 1 shows an interlocking joint in accordancewith the invention which includes anouter leg member 10, an inner legmember 20, and a locking or securingmeans. Leg 10 is an elongated hollowtube having a square cross section. As shown in the end view of FIG. 5,leg 10 includes four sidewalls 11, 12, 13 and 14 which intersect to formfour vertices l5, l6, 17-and 18. Leg 20, which is adapted forlongitudinal insertion into leg 10, includes four interconnected flanges21, 22, 23 and 24 which form an X or cruxiform shape in cross section.The extremities 25, 26, 27 and 28 of each flange, i.e., the furthermostportion of each flange from the intersection of that flange with theremainder of flanges of leg 20, are dimensional so as to extend and fitinto a vertex of leg 10. Thus, extremity 25 of flange 21 extends intovertex 15, extremity 26 of flange 22 extends into vertex l6, and so on.To enable a closer fit, extremities 25, 26, 27 and 28 may be chamferedor tapered, if desired. The securing means, shown in FIGS. l-S is anarcuate spring member 30 including a pair of generally semicircularlobes 31 and 32.. One end 31a,

32a of each lobe may be affixed to one flange (flange,

24 shown) of leg at a point somewhat removed from the extremity 28 ofthe flange by welding or other suit- 4 able fastening means.Alternatively, as shown in the drawing, member 30 may be fabricated froma portion of one convolution of an ordinary helical wire spring.

In this event, member 30 can be affixed to leg 20, i.e., maintained in adesired position with respect to leg 20, simply by forming an aperture40 in flange .24 and by passing spring member 30 about halfway throughthe aperture. The radius of lobes 31 and 32 is chosen to beapproximately equal to the distance between the point of affixation(aperture 40, for example) and the extrernity of the flange adjacentwhich the lobe is positioned. Thus, more specifically, lobe 31, which ispositioned adjacent flange 21, has a radius equal to the distance'between aperture 40 and extremity lobe32, which is positioned adjacentflange 23, has a radius equal to the distance between aperture 40 andextremity 27, which in this case is the same as the radius of lobe 31.The length of each lobe, while approximately semicircular, isnotcritical. As will be seen hereinafter, the length canvary by an amountequal to the width of the flange 24 which intervenes between the flanges21, 23 on which the spring member is positioned, o r sometimes evenmore, without affecting satisfactory operation of the invention.

- Operation of the interlocking joint of FIG. 1 will best be understoodby reference to FIGS. 2-4, which illustrate the relative positionsassumed by the parts of the joint as leg 20 is inserted into leg 10. InFIG. 2, spring member 30 has not yet engaged the sidewalls of outer leg10. Accordingly, depending on the size of member 30, there may be asmall degree of clearance between the free ends 31b, 32b of lobes 31 and32 and flange 24. In FIG. 3, spring member 30 has partially engaged thesidewalls of outer leg 10, as the inner leg is longitudinally insertedtherein. At thispoint, the free ends 31b and 32b of lobes 31 and 32 makeconta'ct withv flange 24, and the force required for continued insertionsubstantially increases. This force persists as leg'20 is furtherinserted in leg 10 so as to fully enclose spring member 30, as shown inFIG. 4. In this position, portions 31c and 3200f lobes 31 and 32 bear onthe interior of sidewalls 11 and 12 of leg 10. This'bearing' or forceurges leg 20 in a direction transverse to its longitudinal axis, asshown in the end view of FIG. 5, since member 30 seeks" to expand intothe widerportion of leg 10 that is occupied by flanges 21 and 23. Thus,flange 26 is urged toward vertex 16 of leg 10. In addition, portions offlanges 21 and 23 are urged toward sidewalls 14 and 13 of leg 10 in thevicinity of vertices 15 and 17, respectively. For purposes ofillustration,

the points of contact are designated 50, 51, 52 and 53,.

it being understood that in reality flanges 21 and 23 as well as flange22 engage the corresponding vertices on longitudinal lines which passthrough points 50, 51, 52

and 53. By virtue of the aforedescribed action, inner leg 20 is held ina desired relative position with respect to outer leg'10. The relativepositions of the legs may be changed when desired, but the frictionforces between flanges 21, 22 and 23 and vertices 15, 16 and 17 must ofcourse be overcome. By way of example only, for an interlocking jointconstruction of extruded aluminum the force typically required toovercome friction is on the order of 50 pounds. Of course, the frictionforces generated in a particular embodiment depend upon the diameter ofspring member 30, and the material from which it and outer leg 10 arecon structed.

As mentioned previously, the length of lobes 31 and 32 of spring member30 may be increased beyond a semi-circular shape without interferingwith proper joint operation. In this event, when leg 20 is insertedwithin leg 10, the free ends 31b and 32b of each spring lobe simplyspread in a longitudinal direction and contact the sides of flange 24 atpoints further removed from points of affixation 31a and 32a. Also,lobes 31 and 32 become somewhat deformed, each assuming an approximatelyhalf-oval shape. However, the holding force between legs and 20 remainsadequate, and can even increase.

It is important to note several minor modifications or adaptations thatcan be made to the interlocking joint arrangement of FIGS. l-S. First,it should be understood that the free ends 31b, 32b of lobes 31 and 32'may be located either forward or rearward of the fixed ends of thelobes, forward being defined as the direction toward which leg 20 ismoved when being inserted in leg 10. Second, it should be apparent thatmore than one spring member such as member 30 may be used,

especially where the assembled joint is relatively long, e.g., longerthan 2 or 3 feet. If multiple securing means are used, they need not beaffixed to the same flange. Third, where a single spring member isutilized, it can be affixed to leg 20 at various points along the legslength, but is advantageously centrally located, so that the holdingforce is more uniformly distributed.

As shown in FIG. 6, another form of locking or securing means that canbe used in lieu of or in addition to spring member 30 is a locking pin60 affixed to one flange 24 of leg 20 and positioned adjacent to atleast another one of the flanges (e.g., flanges 21 and 23). As withspring member 30, affixation of pin 60 may be accomplished by welding orany other suitable technique, or a single pin having two arms 61 and 62may be inserted through an aperture 40a in the flange 24 interveningflanges 21 and 23 upon which the pin is positioned. The length of eachpin arm 61 and 62 is chosen to be approximately equal to the'distancebetween the point of affixation (e.g., aperture 40a) and the extremity25, 27 of the flange on which the pin is positioned.

When inner leg 20 is inserted into outer leg 10, as shown in FIG. 7,arms 61 and 62 are bent rearwardly as their free ends 61a and 62a engagesidewalls 11 and 12, respectively. In a manner analogous to theoperation of spring member 30, the free ends 61a and 62a bear on thesidewalls and urge flange 22 toward vertex 16. In addition, as explainedpreviously, portions of flange 21 and 23 are urged toward sidewalls 14and 13 of leg 10 in the vicinity of vertices 15 and 17, respectively.Thus, leg is held securely'in a desired relative position with respectto leg 10, by the friction forces between flanges 21, 22 and 23 andvertices 15, 16 and 17 as previously described, and as further shown inFIG. 8. However, there is one important difference between locking pin60 and spring member 30: the free ends 61a and 62a of arms 61 and 62 oflocking pin 60, when rearwardly bent, act to grip side-walls 11 and 12and prevent subsequent extraction of inner leg 20 from outer leg 10.This one-way action of the arms of pin 60 results from the fact thatfree ends 160 and 62a can slip over the inner surfaces of leg 10 duringinsertion, but are forced or jammed into the inner surfaces whenextraction is attempted. Insummary, locking pin 60 serves two purposes.During insertion or forward movement, it'bears on the sidewalls of outerleg 10 and urges one or more flanges ofinner leg 20 into frictionalengagement with corresponding vertices; when rearward movement isattempted, its free ends act to engage the sidewalls of leg 10. muchlike a pawl engages a ratchet, and prevents extraction. By way ofexample, the force required for insertion compared to the extractionforce needed to break pin 60 can easily be on the order of 1 to 20.

Referring now to FIGS. 9 and 10, there are shown perspective and endviews, respectively, of anotherembodiment of the instant invention. Inthis arrangement, an interlocking joint includes a tubular hollow outerleg having a triangular cross-section, and an inner leg adapted forlongitudinal insertion therein. Inner leg 100 comprises threeinterconnected flanges 101,

102 and 103 which form a Y-shaped cross-section. Each of the flangesfits within one of the vertices 91, 92 and 93 of outer leg 90. In thisembodiment, a securing means 110 similar to spring member 30 may beaffixed to one flange, e.g., flange 101, and be positioned on adjacentflanges 102 and 103. Affixation may be accom-,

plished by inserting securing means 110 through an aperture 120 formedin flange 101, and the dimensions of securing'means 110 determined. asset out above. As in the afor edescribed embodiment, securing means 110acts to bear on sidewalls 94 and 95 of outer leg 90, and thereby urgethe extremities and 106 of flanges 102 and 103 into engagement withvertices 92 and 93, respectively. Thus, when inserted, leg 100 is heldin a desired relative position with respect to leg 90, as shown clearlyin FIG. 10.

Although securing means 110 is similar to spring member 30, it is notidentical thereto. Securing means 110 is nonplanar, its'lobes 111, 112defining planes which intersect at an angle 0 which corresponds to-theangle formed by flanges 102 and 103. As an alternative, securing means110 can be supplemented orv replaced by a locking pin, not shown,similar to locking pin 60. However, such a locking pin, if fabricatedfroma length of wire having two arms inserted through aperture 120, mustbe V-shaped at an angle 0, so that the arms can assume positionsadjacent to flanges 102 and 103.

Numerous other configurations of elongated inner and tubular hollowouter leg members may also be practiced in accordance with the instantinvention. Each of these arrangements, which are shown in end view inFIGS. 11 through 15, may use securing means similar to spring member 30or locking pin 60.

In FIG. 11, the outer leg 1,110 is rectangular in crosssection. Theinner leg 1,120 includes three interconnected flanges 1,121, 1,122 and1,123 having a T- shaped cross-section each of which extend into avertex of the outer leg, and a fourth flange 1,124 the extremity ofwhich need not contact outer leg 1,110. Flange 1,124 serves only as alocation for affixing securing means 1,130; this flange need not run theentire length of inner leg 1,120, but may instead include one or moreflange-like tabs which hold the securing means in a desired position. Inoperation, this configuration is identical to the one of FIGS, 1-8.Thus, securing means 1,130 bears'on the sidewalls of outer leg 1,110,and urge flanges 1,12l, 1,122 and 1,123 into or toward theircorresponding vertices.

In FIG. 12, the outer leg 1,210 is again rectangular.

each of which extend into a vertex of the outer leg. One

? offset from the remaining diagonal, their intersections with the firstpair of flanges being at different points. In this configuration,securing means 1,230, similar to spring member 30, includes twogenerally semicircular lobes 1,231, 1,232 which have different radii.The radius of lobe 1,231 is approximately equal to the distance betweenthe point of affixation 1,233 to one side of flange 1,221 and theextremity of flange 1,224, and the radius of lobe 1,232 is approximatelyequal to the distance between the point of affixation 1,234 to the otherside of flange 1,221 and the extremity of flange 1,223. Alternatively,if a two armed locking pin similar to locking pin 60 is used, the armswould be of unequal lengths. In either event, the securing means may beaffixed to fl ange 1,221 by insertion through an aperture therein, andserves to bear on the sidewalls of outer leg 1,210 and urge flanges1,222, 1,223 and 1,224 into engagement with their correspondingvertices.

Still other configurations are illustrated in FIGS. 13-15. The operationof each arrangement is similar to that of the aforedescribedembodiments, and will not be described in detail. Suffice it to say thatin the joint of FIG. 13, the outer leg 1,310 is five sided, while theouter legs 1,410 and 1,510 in FIGS. 14 and 15 are hexagonal; In thearrangement of FIG. 13, the inner leg 1,320 is generally T-shaped incross-section, while inner legs 1,420 of FIG. 14 and 1,520 of FIG. 15are similar to'the inner legs shown in FIGS. 12 and 5, respectively. Thesecuring means 1,330, 1,430 and 1,530 in each arrangement may be similarto spring member 30 or locking pin 60. Many other arrangements withdifferent inner and outer leg configurations can also operatesatisfactorily, as will be evident to those skilled in the art.

Although there are many varied uses for the interlocking joint of thepresent invention, it will be instructive to describe one particularapplicationin the field of cubicle fabrication. FIG. 16 illustrates onesuch cubicle," known in the telephone industry as a position, whichpartitions floor space into a small office or complex of offices inwhich employees such as opera tors may "perform their assigned taskswithout interrupting or being interrupted by personnel working inadjacent areas. The position may include a series of baffles or walls1,601, 1,602 and 1,603 which partially surround the working area, andone or more tables or shelves 1,610, 1,611 which are mounted on thewalls. To give a modern and airy appearance, the walls may includetranslucent panels 1,604, 1,605 affixed to the upper portions of thewalls.

Several interlocking joints in accordance with the instant invention areused in constructing the position of FIG. 16. For example, vertical leg1,620 is connected to bat'fle brace leg 1,630 by a two-way cornerassembly 1,640. Legs 1,620 and 1,630 are similar to outer leg 10 ofFIG. 1. Corner assembly 1,640 comprises two leg members 1,641 and 1,642similar to inner leg 20 of FIG. 1, connected at right angles to eachother by a hub 1,643. Affixed to legs 1,641 and 1,642 are securing means1,644, 1,645, respectively, which may be similar to spring member ofFIG. 1. Leg members 1,641 and 1,642 areinserted within legs 1,620 and1,630, respectively, and are held in desired position by the securingmeans, as previously explained. U-shaped channels 8 1,621, 1,631 maybeconnected to one outerwall of legs 1,620 and 1,630, so as to hold panel1,604 in place.

Channels 1,621 and 1,631 can be attached to their re- 'with theinvention. v In a similar manner, 'baffle brace leg 1,630 is connectedto battle brace leg 1,660 and vertical leg 1,670 by a three way cornerassembly 1,680. The latter includes three leg members 1,681, 1,682 and1,683 similar to inner leg 20 of FIG. 1,connected at right angles toeach other at hub 1,684. Each leg includes a corresponding securingmeans 1,691, 1,692 and 1,693.

From the above examples, it will be evident that various combinations ofinterlocking joints in accordance with the invention can be combined toallow interconnection at mutually right angles of up to six outer legsat a single hub. These legs can be used for numerous purposes. It isalso to be noted that a cap member, 1,650 which is simply a one-way hub,can be inserted in a leg such as leg 1,651 to provide the latter with asmooth, finished looking exterior. In this case, it is advisable toemploy a securing means 1,652 similar to locking pin of FIG. 6, so thatonce the cap member is positioned, it-cannot thereafter be extracted. Itwill be apparent from the foregoing that one skilled in the art may makevarious changes and modifications to the apparatus disclosed hereinwithout departing from the spirit and scope of this invention, which isdefined in the appended'claims. I

What is claimed is: 1. An interlocking joint including 1 an outer legmember comprising a hollow elongated tube having a longitudinal axis andat least three side walls, said side walls intersecting to form at leastthree vertices, g

an inner leg rnember adapted for longitudinal insertion into said outerleg, said inner leg member comprising at least three interconnectedflanges each having an extremity extending into a particular one of saidvertices, and

securing means affixed at a point to a first one of said flangesarranged to bear on the interior of at least one of said side walls ofsaid outer leg member, so as to urge at least a second one of saidflanges of said inner leg member toward the corresponding one of saidvertices,

thereby securing said inner leg member in a desired relative positionwith respect to said outer leg member.

2. The invention defined in claim 1 wherein said securing means includesan-arcuate spring member having at least one semicircular lobepositioned adjacent another one of said flanges and having a radiusapproximately equal to the distance between said point of affixation andsaid extremity of said other flange.

3. The invention defined in claim 1- wherein said securing meansincludes a locking pin positioned adjacent another. one of said flangesand having a length approximately equal to the distance between saidpointof affixation and said extremity of said other flange.

4. The invention defined in claim 1 wherein said outer leg member isrectangular in cross section,

said securing means includes an arcuate spring member having twosemicircular lobes each positioned on opposite flanges of said inner legmember, said spring member having a radius approximately equal to thedistance between said point of affixation and said extremity of one ofsaid opposite flanges, and

said first one of said flanges intervenes between said opposite flanges.

5. The invention defined in claim 4 wherein said first one of saidflanges includes an aperture formed therein and said spring member isaffixed to said first one of said flanges by insertion through saidaperture.

6. The invention defined in claim 1 wherein said outer leg member istriangular in cross section and said inner leg member is Y-shaped incross section.

7. An interlocking joint comprising a tubular hollow outer leg having aninterior surface, an inner leg having at least first, second and thirdinterconnected flanges adapted for longitudinal insertion in said outerleg, and

securing means affixed to said inner leg for maintaining said inner legin a desired position with respect to said outer leg by urging ones ofsaid flanges toward said interior surface.

8. The invention of claim 7 wherein said securing means includes anarcuate spring member having at least one generally semicircular lobeaffixed to said first flange and positioned adjacent said second flange.

9. The invention defined in claim 7 wherein said first flange includesan aperture formed therein, said securing means includes an arcuatespring member having two generally semicircular lobes, and

said spring member is affixed to said first flange by insertion throughsaid aperture.

10. The invention defined in claim 7 wherein said securing meansincludes a locking pin affixed to said first flange and positionedadjacent to said second flange, the length of said pin beingapproximately equal to the width of said second flange.

11. In an interlocking joint comprising a first rectangular hollow leg,a second X-shaped leg including four mutually perpendicular flanges,said second leg adapted for longitudinal insertion in said first legwhereby opposite pairs of said flanges are positioned along the crosssectional diagonals of said first leg, means for securing said secondleg in said first leg, said securing means including an arcuate springmember positioned on one planar surface formed by one of said pairs ofopposite flanges and affixed to the one of said flanges intervening saidpair of opposite flanges.

12. The invention defined in claim 11 wherein said intervening flangeincludes an aperture formed therein and said spring member is insertedin said aperture. I

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION- Patent No.3,825,355 Dated July 23, 197

Inventor(s) Eran}; H Martin It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

A line has been omitted aftef "toward" on line 15, after "toward" add:

--their corresponding vertices. The securing means can be-. 7 ,e-

Column 5, line 63, "16a" should read --61a Signed and sealed this 19thday of November 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents po'wso Y 1 I USCOMM-DC scan-Pea i ".5. GOVIRMIINT PRINTINGOFFICI "I! 0-Sli-3S4.

1. An interlocking joint including an outer leg member comprising ahollow elongated tube having a longitudinal axis and at least three sidewalls, said side walls intersecting to form at least three vertices, aninner leg member adapted for longitudinal insertion into said outer leg,said inner leg member comprising at least three interconnected flangeseach having an extremity extending into a particular one of saidvertices, and securing means affixed at a point to a first one of saidflanges arranged to bear on the interior of at least one of said sidewalls of said outer leg member, so as to urge at least a second one ofsaid flanges of said inner leg member toward the corresponding one ofsaid vertices, thereby securing said inner leg member in a desiredrelative position with respect to said outer leg member.
 2. Theinvention defined in claim 1 wherein said securing means includes anarcuate spring member having at least one semicircular lobe positionedadjacent another one of said flanges and having a radius approximatelyequal to the distance between said point of affixation and saidextremity of said other flange.
 3. The invention defined in claim 1wherein said securing means includes a locking pin positioned adjacentanother one of said flanges and having a length approximately equal tothe distance between said point of affixation and said extremity of saidother flange.
 4. The invention defined in claim 1 wherein said outer legmember is rectangular in cross section, said inner leg member isX-shaped in cross section, said securing means includes an arcuatespring member having two semicircular lobes each positioned on oppositeflanges of said inner leg member, said spring member having a radiusapproximately equal to the distance between said point of affixation andsaid extremity of one of said opposite flanges, and said first one ofsaid flanges intervenes between said opposite flanges.
 5. The inventiondefined in claim 4 wherein said first one of said flanges includes anaperture formed therein and said spring member is affixed to said firstone of said flanges by insertion through said aperture.
 6. The inventiondefined in claim 1 wherein said outer leg member is triangular in crosssection and said inner leg member is Y-shaped in cross section.
 7. Aninterlocking joint comprising a tubular hollow outer leg having aninterior surface, an inner leg having at least first, second and thirdinterconnected flanges adapted for longitudinal insertion in said outerleg, and securing means affixed to said inner leg for maintaining saidinner leg in a desired position with respect to said outer leg by urgingones of said flanges toward said interior surface.
 8. The invention ofclaim 7 wherein said securing means includes an arcuate spring memberhaving at least one generally semicircular lobe affixed to said firstflange and positioned adjacent said second flange.
 9. The inventiondefined in claim 7 wherein said first flange includes an aperture formedtherein, said securing means includes an arcuate spring member havingtwo generally semicircular lobes, and said spring member is affixed tosaid first flange by insertion through said aperture.
 10. The inventiondefined in claim 7 wherein said securing means includes a locking pinaffixed to said first flange and positioned adjacent to said secondflange, the length of said pin being approximately equal to the width ofsaid second flange.
 11. In an interlocking joint comprising a firstrectangular hollow leg, a second X-shaped leg including four mutuallyperpendicular flanges, said second leg adapted for longitudinalinsertion in said first leg whereby opposite pairs of said flanges arepositioned along the cross sectional diagonals of said first leg, meansfor securing said second leg in said first leg, said securing meansincluding an arcuate spring member positioned on one planar surfaceformed by one of said pairs of opposite flanges and affixed to the oneof said flanges intervening said pair of opposite flanges.
 12. Theinvention defined in claim 11 wherein said intervening flange includesan aperture formed therein and said spring member is inserted in saidaperture.